Field of the Invention
The present invention relates to a rotation driving mechanism for windmill, which is used in a windmill including a base-side structure and a rotation-side structure that is rotatable with respect to the base-side structure, so as to rotate the rotation-side structure with respect to the base-side structure.
Background Art
As a windmill used as a wind turbine generator, a windmill including a nacelle and blades have been conventionally used. The nacelle is rotatably disposed on top of a tower, and a generator and so on is disposed in the nacelle. The blades are disposed rotatably with respect to a hub provided on the nacelle. In such a windmill, a rotation driving mechanism configured to rotate the nacelle (rotation-side structure) with respect to the tower (base-side structure) is used.
For example, JP2013-083247A discloses a rotation driving mechanism including a yaw driving mechanism fixed on a nacelle and a ring gear fixed on a tower, wherein a pinion of the yaw driving mechanism is meshed with the ring gear. In the rotation driving mechanism, when the yaw driving mechanism work, the pinion makes a rotation while being meshed with the ring gear as well as makes a revolution, so that the nacelle (rotation-side structure) is rotated with respect to the tower (base-side structure).
In the aforementioned rotation driving mechanism, since the number of teeth of the pinion and the ring gear, which simultaneously contact with each other, is small, a large stress is generated in a drive transmission area between the pinion and the ring gear. This not only reduces a mechanism life of the rotation driving mechanism, but also impairs a drive transmission capacity of the mechanism. On the other hand, in order to elongate the mechanism life and to improve the drive transmission capacity, the rotation driving mechanism has to be enlarged in size.